Keller C H
Scripps Institution of Oceanography, University of California, San Diego, La Jolla 92093.
J Comp Physiol A. 1988 Apr;162(6):747-57. doi: 10.1007/BF00610964.
Neuronal reliability and sensitivity to behaviorally relevant stimulus patterns were investigated in a higher-order nucleus of the diencephalon believed to participate in the jamming avoidance response (JAR) of the weakly electric fish, Eigenmannia. The fish raises or lowers its frequency of electric organ discharge (EOD) to minimize interference from a neighboring fish's EOD. Proper JARs require determination of the sign of the difference frequency (Df) between the neighboring fish's EOD and the fish's own EOD. Bastian and Yuthas (1984) recently described diencephalic neurons within the nucleus electrosensorius that are able to make this determination. In the present study, response properties of such neurons were compared with those of lower-level 'sign-selective' cells found in the torus semicircularis and the optic tectum (Heiligenberg and Rose 1985) as well as with properties of the intact behavior. Most sign-selective cells within the nucleus electrosensorius show a high degree of selectivity for one sign of the difference frequency; cells with either sign preference were found in approximately equal numbers. The sign preference and the degree of sign selectivity is most often independent of the spatial orientation of the jamming stimulus. In contrast, the responses of toral and tectal cells are less robust and consistent and are often highly dependent on the geometry of the jamming stimulus. Determination of the sign of the difference frequency requires the analysis of amplitude modulations coupled with modulations in phase (timing) differences between pairs of areas of the body surface. The most sensitive cells recorded in the nucleus electrosensorius can determine the sign of the difference frequency with timing differences of 1 microsecond or less, roughly comparable to the behavioral threshold of 400 ns (Carr et al. 1986). The best toral/tectal response required at least a 16 microseconds modulation. Cells within the nucleus electrosensorius thus code the sign of Df with a high degree of reliability and sensitivity. Ambiguities persist, however, which suggest that single cells at this level cannot completely account for the behavioral discrimination. Additional processing may be necessary to transform a still primarily sensory code into a motor program for control of the JAR (Rose et al. 1988).
在间脑的一个高级核团中，研究了神经元的可靠性以及对行为相关刺激模式的敏感性。该核团被认为参与弱电鱼裸背鳗的干扰回避反应（JAR）。这种鱼会提高或降低其电器官放电（EOD）的频率，以尽量减少来自相邻鱼的EOD的干扰。正确的JAR需要确定相邻鱼的EOD与自身EOD之间的差频（Df）的符号。巴斯蒂安和尤塔斯（1984年）最近描述了电感受核内的间脑神经元，它们能够做出这种确定。在本研究中，将这类神经元的反应特性与在半规管隆起和视顶盖中发现的较低级别的“符号选择”细胞的反应特性（海利根贝格和罗斯，1985年）以及完整行为的特性进行了比较。电感受核内的大多数符号选择细胞对差频的一种符号表现出高度的选择性；具有两种符号偏好的细胞数量大致相等。符号偏好和符号选择性的程度通常与干扰刺激的空间方向无关。相比之下，半规管隆起和顶盖细胞的反应不太稳健和一致，并且通常高度依赖于干扰刺激的几何形状。确定差频的符号需要分析幅度调制以及体表区域对之间相位（时间）差的调制。在电感受核中记录到的最敏感细胞能够以1微秒或更短的时间差确定差频的符号，这大致与400纳秒的行为阈值相当（卡尔等人，1986年）。半规管隆起/顶盖的最佳反应至少需要16微秒的调制。因此，电感受核内的细胞以高度的可靠性和敏感性编码Df的符号。然而，仍存在一些模糊性，这表明这个层面的单个细胞不能完全解释行为辨别。可能需要额外的处理，将仍然主要是感觉编码的信息转化为用于控制JAR的运动程序（罗斯等人，1988年）。
